Wearing ocular prostheses, for example, flexible or hard contact lenses, without harm to the cornea or conjunctival metabolism requires resolution of the problem of eye intolerance. To overcome the problem of intolerance, one of ordinary skill in the art at the time of fitting of the prosthesis executes various tolerance tests, including tests for the quality and quantity of tears, for controlling the centering and displacement of the prosthesis on the eye, and for observing the lacrymal film present under the prosthesis. Certain of the tests are effected with the aid of a light source emitting ultraviolet and invisible rays, particularly in the blue range, that excite a fluorescent substance dropped into the eye to emit a visible radiation. Accordingly, the circulation of the lachrymal film under the lens and zones of small lacrymal quantity can be observed.
Despite satisfactory results indicated by these tests, an ocular prostheses may ultimately be ill-tolerated by the person who wears them. Moreover, one of ordinary skill in the art can never determine with certainty the type of prosthesis best suited for a particular person. Cases may arise where sufficiently well-tolerated prostheses may be replaced by other types yielding even greater tolerance.